The Hydro Guardian biosensor was developed with the aim of creating a sensitive and multifunctional instrument for the detection of antibiotics and heavy metals in water samples. Our strategy started with the identification of possible molecular indicators that would enable the detection of these two different types of contaminants. We decided on a design approach that included elements from both prokaryotic and eukaryotic systems to maximise flexibility and functionality. For the detection of antibiotics, we used a system that mimics bacterial resistance mechanisms, while for heavy metals we used metal-responsive elements that are well conserved in different species.